The present invention relates generally to hand trucks, and, more particularly, to hand trucks having motorized stair climbing capability.
Hand trucks are generally well known and typically have a ladder-like frame having a handle at a top end and wheels at a bottom end thereof. A generally perpendicular platform or plate typically extends from the frame proximate the bottom end. The platform is typically used to support objects during transportation thereof using the hand truck.
Stair climbing hand trucks are also generally known. Typically, such stair climbing hand trucks include some form of motorized stair climbing mechanism. Typically, stair climbing mechanisms include an electrically powered motor having an output shaft which is drivingly connected to stair climbing feet. The feet are generally rotatable about a path which allows the feet to be placed on successive stairs in a flight of stairs, allowing the mechanism to lift the hand truck up one stair at a time until the hand truck reaches the top of the flight of stairs.
A typical problem with such conventional stair climbing hand trucks is that they have only one connection between the output shaft and the rest of the stair climbing mechanism. Because of this, if a failure of the drive connection occurs (i.e., a belt or chain drivingly connecting the output shaft with the rest of the stair climbing mechanism breaks or otherwise fails), the stair climbing hand truck, having no redundant or backup system, is left powerless. If the failure occurs during stair climbing, the powerless hand truck is left to potentially fall down the stairs. This creates a potentially dangerous situation to the operator of the stair climbing hand truck, who could potentially be dragged down the stairs by the falling hand truck, as well as anyone who happens to be following the stair climbing hand truck up the stairs.
Therefore, it is desirable to have a stair climbing hand truck with a redundant drive system, such as an output shaft that has two drive connections that drivingly engage the rest of the stair climbing mechanism. In this way, if one of the drive connections between the output shaft and the rest the stair climbing mechanism were to break, because of the continued operation of the second drive connection, the stair climbing hand truck would not be rendered powerless.